Ptychopera unicornis, Van Steenkiste & Leander, 2018

Van Steenkiste, Niels W. L. & Leander, Brian S., 2018, Molecular phylogeny of trigonostomine turbellarians (Platyhelminthes: Rhabdocoela: Trigonostomidae), including four new species from the Northeast Pacific Ocean, Zoological Journal of the Linnean Society 182, pp. 237-257 : 251-252

PTYCHOPERA UNICORNIS SP. NOV.

( FIG. 6B, C–E)

Etymology: The species epithet refers to the single, horn-like spine in the bursa.

Type locality: Clover Point , Victoria, British Columbia, Canada (48°24 ′ 12 ″ N, 123°21 ′ 03 ″ W), algae in rocky lower intertidal (02/09/2016; 03/03/2016) .

Type material: One whole mount which is designated as the holotype ( SMNH Type-8921) .

Other material: Observations on three live animals. 18S rRNA (GenBank accession # MF321752 ), 28S rRNA (GenBank accession # MF321761 ) .

Diagnosis: Species of Ptychopera with 46- μ m-long stylet. Stylet consists of two slightly curved tubes. One tube is longer and club-shaped, the other one is shorter and triangular. Mantle with rounded plate and serrated edge. Bursa with sclerotized folds and an 8- μ m-long spine.

Description: Live animals mostly transparent and measuring about 0.5–0.7 mm ( Fig. 6B). General appearance typical of species of Ptychopera with the pharynx in the first half of the body and oblong rhabdites in the epidermis.

Internal organization ( Fig. 6E) almost identical to P. japonica and other species of Ptychopera , the only difference being the somewhat more posterior position of the pharynx, the size and construction of the stylet and the presence of a spine in the proximal half of the bursa. The slightly curved stylet consistently measures 46 μ m (x = 46 μ m; n = 4) and is composed of two slightly curved tubes or plates surrounded by a folded sclerotized mantle of which the distal half forms a large rounded plate with a slightly serrated convex edge ( Fig. 6C, D). The two curved tubes differ in length and form. The longer tube on the concave side of the stylet is club-shaped with a rounded distal end while the shorter tube on the convex side of the stylet is more triangular and pointed. The bursa has a slightly sclerotized bursal membrane with sclerotized folds and an 8- μ m-long spine at its base ( Fig. 6C–E).

Discussion: Although the stylet of P. unicornis sp. nov. resembles the stylet of P. japonica , it differs by its smaller size, the more rounded serrated plate, the lack of an extended spur on the mantle, and a marked difference between the form and length of the two slightly curved stylet tubes. P. unicornis sp. nov. also has a spine in the proximal part of the bursa while P. japonica clearly lacks this. Sclerotized folds and ridges in the bursa are common in Ptychopera , but only three other species, P. avicularis Karling, 1974 ; P. spinifera Den Hartog, 1966b ; and P. purasjokii Ax, 1971 , have a single proper spine or teeth at the basis of the bursa. However, these species differ from P. unicornis sp. nov. by their stylet morphology.

In addition to differences in stylet morphology, P. unicornis sp. nov. and P. japonica seem to prefer different kinds of intertidal habitats. P. unicornis sp. nov. was found on algae in the marine rocky intertidal, while P. japonica has a preference for slightly brackish intertidal mudflats.

PROMESOSTOMIDAE DEN HARTOG, 1964 BRINKMANNIELLINAE LUTHER, 1948 TVAERMINNEA LUTHER, 1943

Tvaerminnea Luther, 1943: 81 ; Luther, 1948: 36; Luther, 1962: 44.

Diagnosis (amended from Luther, 1962): Brinkmanniellinae with long, stretchy body. Copulatory organ consists of a proximal copulatory bulb filled with sperm, a middle part containing the ejaculatory duct, and a distal stylet. Stylet is a short tube, with transversal folds and a complex hookshaped distal end. Bursa with proximal, tooth-like folds of the basal membrane.

Type species: Tvaerminnea karlingi Luther, 1943 .